Eye-trackers are instruments for measuring the movements of an eye. An eye-tracker communication system allows a physically handicapped person to use eye movements to communicate. There are several varieties as explained in "Survey of Eye Movement Recording Methods" by Young and Sheena, Behavorial Research Methods Instrumentation, 175, Vol. 7 (5), pages 397-429. A number of eye-tracking devices have been explained in the patent literature including U.S. Pat. Nos. 2,288,430; 2,445,787; 3,462,604; 3,514,193; 3,534,273; 3,583,794; 3,806,725; 3,864,030; 3,992,087; 4,003,642; 4,034,401; 4,075,657; 4,102,564; 4,145,122; 4,169,663; and 4,303,394.
One technique, the theory of which is explained in the Young and Sheena article, is the corneal reflection technique. The corneal reflection technique can be implemented in a number of ways. See, Laboratory Oculometer, NASA CR-1422 by John Merchant and "Eye Fixations Recorded on Changing Visual Sense by the Television Eye Marker" by Mackworth and Mackworth in Journal of Optical Society of America, Vol. 48, No. 7, July 1958.
While the prior art discloses eye-tracking devices, the applicants found that there was no relatively inexpensive eye-tracking system and technique which could be used by individuals on a more or less continual basis. Prior systems have been large and expensive, if adequate.
While it has been possible to use a digitized image processed by computer to implement the corneal reflection eye-tracking technique, it has required a very large, very fast computer to do so. Consider that a television frame divided into 240 lines by 256 pixels (picture elements) requires nearly 62,000 bytes of memory if one byte is stored for each pixel. Moreover, the time to load and compare and analyze 62,000 bytes of memory in a typical eight bit microprocessor would be no less than several seconds--too long for any value in a real time eye-tracking device.
Some form of digital preprocessing is essential if eight bit or even sixteen bit microprocessors clocked at typical rates are to be used in a practical eye-tracker. A preprocessing frame grabber is disclosed in "Video Signal Input" Robotics Age, March/April 1981, pages 2-11 and 19. The article describes a circuit for comparing video signals to an analog threshold (programmable at 256 levels) to establish one bit of data for each pixel and then packing the data (eight pixels to the byte) before dispatching each data byte one at a time to the associated computer memory. Eight thousand (8K) bytes of computer memory are required for one frame. Since only one bit of data for each pixel is gathered, a simple binary image is gathered which is insufficient for most computer vision applications. It is clearly insufficient for eye-tracking by the corneal reflection technique where it is necessary to locate the corneal reflection (the brightest location on the frame) and the pupil (either very dark or less bright than the corneal reflection). Moreover, eight thousand bytes (8K) of data is still a large quantity for real time processing. Consider that eye movements can take only fractions of a second.